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RISS 인기검색어
- 검색키워드
- 저자 : Habib Shahnazari (검색결과 3 건)
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Habib Shahnazari,Hossein Salehzadeh,Reza Rezvani,Yasser Dehnavi 대한토목학회 2014 KSCE JOURNAL OF CIVIL ENGINEERING Vol.18 No.4
Laboratory research was conducted to compare the monotonic behavior of two different marine calcareous sands - Hormuz Island(HI) and Bushehr Port (BP) - with siliceous sand named Firoozkuh sand (F). A series of undrained isotropically consolidated triaxialtests was performed on reconstituted specimens of these sands. In this experimental investigation, their contractive and dilativebehaviors were evaluated. The effect of some important parameters, such as relative density and confining pressure on the behaviorof these specimens was studied. To analyze the effect of shape and stiffness (resistance to particle breakage) on the contractive andthe dilative responses of these soils, the influence of axial strain on the crushability of the calcareous soils was assessed. Thereafter,the undrained behavior of the soils was analyzed, using two parameters, which represented a normalized variation of excess porewater pressure in two phases of monotonic triaxial tests. The contractive and dilative behavior of the two different calcareous sandswas compared to the siliceous sand. The results showed that particle shape played a key role in the behavior of soils in contractivephase. However, the shearing response of the used carbonate soils was more affected by particle crushing in dilation.
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Effect of Cyclic Pre-straining on the Dynamic Behavior of Very Dense Sand
Habib Shahnazari,Ali Akbar Heshmati,Hossein Sarbaz 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.1
Earthquakes, including the main shock, fore-shocks and after-shocks, are among the most devastating natural disasters. Mostbuilding structures that are damaged due to a main shock then experience more damage when they are subjected to aftershocks. Anystrong shock may decrease the strength of a steel or concrete structure. However, depending on its magnitude, a foreshock may eitherincrease or decrease the shear strength of an earth-fill structure. A loose granular specimen usually gains some shear strength whensubjected to pre-loading. This behavior is mainly due to an increase in relative density and experience of shear history. For a verydense granular material, it is unclear whether fore-shocks and main shocks increase or decrease its shear strength. However, theanswer to this uncertainty is vital when evaluating the safety factor of a well-compacted granular earth-fill dam after an earthquake. The objective of this study is to study the effects of cyclic pre-straining on the dynamic behavior of saturated and very dense sandspecimens. The major findings from the laboratory study are the following: (a) under small pre-strain, the microstructure remainsessentially unchanged, but an increase in density leads to an increase in the soil strength; and (b) under large pre-strain, themicrostructure is completely altered to a new form. In this case, if the loading amplitude is identical to the one in the previous prestrain,the soil strength increases; however, if the loading amplitude is less than the previous pre-strain, the strength decreases in thenext stage. Such a decrease occurs even though the relative density increases.
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Habib Shahnazari,Mohammad A. Tutunchian 대한토목학회 2012 KSCE Journal of Civil Engineering Vol.16 No.6
This study proposes an innovative mathematical formula that uses multigene Genetic Programming (GP), a recently developed soft computing technique, to predict the ultimate bearing capacity of shallow foundations on cohesionless soils. The real performance of previously developed approaches is also investigated. The multigene GP-based formula was calibrated and validated using an experimental database consisting of approximately one hundred load tests. One half of the data was obtained from full-scale foundations and the other half was obtained from small-scale laboratory footing load tests. The results revealed that the proposed formula by multigene GP could predict the ultimate bearing capacity precisely under the described conditions with a coefficient of correlation of about 98%. Additionally, a comprehensive parametric study on the proposed multigene GP-based formula was conducted to confirm the new methodology’s geotechnical aspects.
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